Microstructure analysis of iron spots on Qinghua porcelain from Jingdezhen imperial kiln

Iron spots as a characteristic of early Qinghua porcelain is closely related to cobalt pigment and manufacturing technology. However, the microstructure of iron spots has not been fully investigated. Seventeen Qinghua samples with iron spot excavated in Jingdezhen imperial kiln were observed under stereomicroscope and SEM. Then, four representative sherds were systematically analyzed using FIB-TEM-EDX. Some ferrite solid solutions (CoFe2O4-Fe3O4 and Mn3O4-MnFe2O4-Fe3O4) are identified. CaFeAlSiO6 and Na2Al2Si2O6-CaAl2Si2O6 continuous solid solutions, as the main crystallites of iron spot are first reported. Moreover, we proposed that the dramatic increase of Fe or Mn in iron spot is caused by the source or formular change of cobalt pigment. Varieties of morphologies and species of the iron spots in Hongwu and Xuande reign implies that technology is under a transition period for adapting new formular, which provide a new perspective to discuss the use of cobalt pig-ments and technology development of Qinghua porcelain.

Automated summary

Iron spots in early Qinghua porcelain, closely related to cobalt pigment and manufacturing technology, have not been fully investigated in terms of microstructure. By analyzing Qinghua samples from the Jingdezhen imperial kiln, ferrite solid solutions were identified, along with the main crystallites of iron spots being reported for the first time. The significant increase in iron or manganese in iron spots was found to be caused by changes in the source or formula of cobalt pigment. The variations in morphology and species of iron spots during the Hongwu and Xuande reigns suggest a transitional period in technology, providing new insights into the use of cobalt pigments and the technological development of Qinghua porcelain.